1. Field of the Invention
The present invention relates to an intrabody introduced device, which is introduced into a test body, or a medical device including the intrabody introduced device. This type of intrabody introduced device includes, for example, a swallowable capsule type endoscope.
2. Description of the Related Art
In recent years, a capsule type endoscope having an imaging function and a wireless function has emerged as one of the intrabody introduced devices in the endoscope area. The capsule type endoscope is swallowed by a test subject as a test body for observation (examination) and then moves inside the stomach, the small intestine, or other organs (in the body cavity) by the organs' peristaltic motion for the observation period until it is excreted naturally from the test subject. The capsule type endoscope sequentially takes images of the inside of the test body by using the imaging function while it moves inside the body cavity.
Image information captured in the body cavity by the capsule type endoscope during the observation of the organs while moving inside thereof is transmitted to an external device provided outside the test body by using a wireless function (radio communication or the like) of the capsule type endoscope and then stored in a memory provided inside the external device. The test subject carries the external device, whereby the test subject is not restrained in behavior during the observation period until the capsule type endoscope is excreted after the test subject swallows the capsule type endoscope. After the observation, images of the inside of the body cavity are displayed on a screen of a display or the like on the basis of the image information stored in the memory of the external device, whereby a doctor or a nurse can make a diagnosis.
In this type of capsule type endoscope, there is a swallowable capsule type endoscope such as, for example, one disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-345743. This capsule type endoscope includes a battery for power supply and an LED for emitting an illumination light by means of the power supplied from the battery. The capsule type endoscope then takes images of the inside of the test body illuminated by the illumination light by using an imaging device to acquire the image information and wirelessly transmits the image information from a transmitter circuit. In the aforementioned capsule type endoscope, the image information is composed of a frame and it is wirelessly transmitted with a horizontal synchronizing signal and a vertical synchronizing signal added at the beginning of the image frame. With synchronization based on the synchronizing signals, a receiver distinguishes the beginning of the image line for scanning the image information when capturing the images.
The capsule type endoscopes of the prior art can incorrectly recognize synchronizing signals as image information, and in such case, may use the synchronizing signals having signal patterns included in the image information. Accordingly, signals in a low-frequency band lower than the frequency of the image information are used as synchronizing signals in some cases. If the frequency band of the synchronizing signals is set to the foregoing frequency band (in the low-frequency band), however, a phenomenon of a fluctuation in the DC level of the signals appears.
Therefore, when the synchronizing signals are binarized at a predetermined level (a threshold value), a margin of the threshold is decreased due to the fluctuation of the DC level, so the receiver has a difficulty to binarize the synchronizing signals.
This invention has an object to provide an intrabody introduced device in which its synchronizing signals are well binarized in the receiver and good quality of images can be obtained.